The present invention relates to an electromagnetic contactor in which the high temperature gas or molten metal formed upon interruption of a current is cooled with a porous metal.
A conventional electromagnetic contactor in which a high temperature gas or molten metal is cooled with porous metal is constructed, for instance, as shown in FIG. 1. In the contactor of FIG. 1, the right and left halves are symmetrical with respect to each other, and hence only the right half is shown in detail.
As shown in FIG. 1, a stationary iron core 12 is fixedly mounted on a mounting stand 10 substantially at the center of the contactor. The mounting stand 10 is made of an insulating material, and the iron core 12 is formed by laminating silicon steel plates. A movable iron core 14 formed by laminating silicon steel plates is provided above the stationary iron core 12. The movable iron core 14 has an associated tripping spring (not shown). An operating coil 16 is wound on the stationary iron core 12. When current is applied to the operating coil 16, the movable iron core 14 is attracted by the stationary iron core 12 against the elastic force of the spring by the action of the electromagnet.
The movable iron core 14 is vertically movably supported on a cross bar 18 made of an insulating material and which has formed therein a square window 18a. A movable contact piece 20 is inserted into the square window 18a of the cross bar 18. A movable contact 22 is formed on one end of the contact piece 20. A spring 24 is elastically inserted between the part of the movable contact piece 20 which is inserted into the square window 18a and the cross bar 18.
A stationary contact 26 is arranged in such a manner as to confront the movable contact 22. More specifically, the stationary contact 26 is fixedly mounted on the substantially U-shaped end portion of a stationary contact piece 28. As the movable iron core 14 is moved vertically, the movable contact 22 is also moved vertically into or out of engagement with the stationary contact. The stationary contact piece 28 extends over a base 30 in the rightward direction in FIG. 1. The exposed part of the stationary contact piece 28 is a terminal section which has a terminal screw 34 through which the contactor is connected to an external circuit.
The movable contact piece 20 and a part of the stationary contact piece 28 are provided in an arc-extinguishing chamber 40 with partition walls 36 and 38 made of an insulating material. The partition wall 36 has a plurality of through-holes 42 through which high temperature gas or molten metal particles produced at the interruption of current are discharged to the outside. An absorbing member 44 made of porous metal is laid on the inner surface of the partition wall 36.
A commutation electrode 46 is provided near the movable contact 22 and an arc runner 48 is arranged near the stationary contact 26. A plurality of magnetic metal arc-extinguishing plates 50 for pulling and extinguishing an arc A.sub.1 are provided extending parallel to the surfaces of the stationary contact piece 28 and the stationary contact 26. That is, the plates 50 are arranged in a direction perpendicular to the direction in which the movable contact piece 20 is moved away from the stationary contact piece 28. Accordingly, the arc A.sub.1 produced upon between the movable contact 22 and the stationary contact 26 is extinguished while moving through states indicated by A.sub.2, A.sub.3 and A.sub.4 in FIG. 1.
The operation of the electromagnetic contactor thus constructed will now be described.
Under the condition that the movable contact 22 is in contact with the stationary contact 26, current is applied to the coil 16 and the movable iron core 14 is attracted by the stationary iron core 12. When, under this condition, application of the current to the coil 16 is suspended, the movable iron core 14 is moved away from the stationary iron core 12 by the action of the tripping spring (not shown), and accordingly the movable contact 22 is disengaged from the stationary contact 26. As a result, an arc A.sub.1 is produced between the contacts. The arc A.sub.1 thus produced is shifted into the space between a commutation electrode 46 and the arc runner by the attracting magnetic action of the metal arc-extinguishing plates 50 and the magnetic force of the currents flowing in the movable contact piece 20 and the stationary contact piece 28; that is, the arc A.sub.1 becomes an arc A.sub.2 in this space. The arc A.sub.2 is moved to the right in FIG. 1, becoming an arc A.sub.3 and then an arc A.sub.4. Thus, the arc, being cut and cooled by the metal arc-extinguishing plates 50, is extinguished.
During the period of time between the production and extinction of the arc, the ambient air is ionized, producing a high temperature gas, while the surrounding metal parts are made molten and are evaporated. The high temperature gas and the molten metal are discharged to the outside through the through-holes 42 in the partition wall 36 as the pressure in the arc-extinguishing chamber 40 increases. In this operation, the high temperature gas is reduced as the gas passes through the absorbing member 44, and the molten metal particles stick to the absorbing member 44.
The existence of the high temperature gas or the molten metal particles reduces the insulating effect in the arc-extinguishing chamber 40. However, as the high temperature gas is cooled by the absorbing member 44 and discharged and the molten metal particles are absorbed by the absorbing member 44, the insulating effect in the arc-extinguishing chamber 40 is recovered, and therefore the interruption performance is improved. Furthermore, external short-circuiting and damage to external parts due to the high temperature gas and molten metal particles are prevented.
However, the conventional electromagnetic contactor is disadvantageous in the following points: When a large current is interrupted repeatedly with the contactor, a part of the absorbing member 44 may be made molten by the molten metal particles, thus forming a through-hole 52 in the absorbing member 44. If a throughhole 52 is formed in the absorbing member 44, then the latter cannot sufficiently cool the high temperature gas or the molten metal particles and cannot satisfactorily prevent the entrance of dust into the arc-extinguishing chamber 40.